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FQXI ARTICLE

July 2, 2016

The Myth of Gravity

A new model in which gravity is not a fundamental force could—counterintuitively—give a controversial quantum gravity theory a boost. It may also change our picture of spacetime, and do away with dark energy.

April 24, 2010

Erik Verlinde

University of Amsterdam

Gravity may be the force that we are most familiar with in everyday life, but physicists do not yet understand its origin. Newton told us that apples fall towards Earth with an acceleration that depends on the Earth’s mass, the apple’s mass, and its distance from the centre of the Earth, while Einstein described gravity by the warping of the fabric of spacetime. But while these theories describe how gravity works, they don’t explain how it arises.

Verlinde, a string theorist at the University of Amsterdam in the Netherlands, believes that the key to understanding gravity is "information." He was inspired by early work on information storage in black holes by Stephen Hawking and Nobel laureate Gerard ’t Hooft. "When I was about fifteen I saw them on television talking about the physics of elementary particles and black holes," says Verlinde. "I knew then that I wanted to work in that area."

The Television Event Horizon

Hawking and ’t Hooft had both worked on the so-called

Entropic force?

Imagining a particle near a spherical holographic screen

allows you to derive Newton’s law of gravity.

It might sound like re-inventing the wheel, but the approach implies that gravity is nothing more than the result of a system maximising its entropy, or disorder. At first glance, this looks like bad news for the quantum gravity crowd. If gravity is an "entropic force," there is no longer a need for physicists to attempt to reconcile general relativity with quantum mechanics, or hunt for the hypothetical

Quantum Threads

However, not all gravity researchers take that view. Smolin, a long term proponent of loop quantum gravity (LQG), believes that Verlinde’s work is not only compatible with LQG, it could even help to explain how familiar Newtonian gravity might emerge in this picture. According to LQG, spacetime isn’t the smooth fabric that Einstein envisioned; rather, if you zoom down to scales of 10

Smolin notes that Verlinde’s model is tied to earlier work by FQXi member Ted Jacobson, who had shown in 1995 that Einstein’s equations of general relativity could be derived using thermodynamics and the holographic principle. "The wonderful thing about the arguments of Jacobson and Verlinde is they give a deep reason for why a quantum theory of gravity should yield the phenomena of gravitation," Smolin writes in his recent paper (arXiv:1001.3668v2).

There isn’t a fundamental

gravitational interaction.

Is that crazy enough?

gravitational interaction.

Is that crazy enough?

- Paul Frampton

If such derivations of dark energy stand up then Verlinde’s ideas "could in some sense complete general relativity," says physicist Sabine Hossenfelder at the Nordic Institute of Theoretical Physics in Sweden. However, there is still a long way to go before physicists will abandon the notion that gravity is a real force as there are several things that remain vague in Verlinde’s formulation, she adds.

Frampton, however, is convinced that Verlinde is on the right track. "I believe that gravity is entirely explained by increases in entropy; there isn’t a fundamental gravitational interaction," he says. "That’s the bottom line. Is that crazy enough?"

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ANONYMOUS wrote on June 1, 2016

How does the objects interact? What decides whether to attract or repel each other?

How does the objects interact? What decides whether to attract or repel each other?

ANONYMOUS wrote on April 21, 2016

Does this mean that if a large hollow body was placed in space it's"gravity" for lack of understanding, could be equal to that of say..... Earth? Random virtual particles pressing onto the surface from all regions of space? "Gravity" being equal on the inside of the sphere to"gravity" on the outside perhaps? I'm struggling with practical application of this theory, though tantalizing to the imagination.

Does this mean that if a large hollow body was placed in space it's"gravity" for lack of understanding, could be equal to that of say..... Earth? Random virtual particles pressing onto the surface from all regions of space? "Gravity" being equal on the inside of the sphere to"gravity" on the outside perhaps? I'm struggling with practical application of this theory, though tantalizing to the imagination.

KAMILLA KAMILLA wrote on April 10, 2016

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192.168.l.254

This is my first time visit here. From the tons of comments on your articles,I guess I am not only one having all the enjoyment right here!

192.168.l.254

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